Holographic sights

Holographic Sight Dots for Quick Action and Demanding Situations.

Differences Between Red Dot and Holographic Sight

Image: Holo vs Red Dot, Eotech.

A holographic sight includes many mirrors compared to a red dot, which generally results in a more expensive and complex product, whereas a red dot is simpler and typically more affordable. 

In a holographic sight, at least in theory, the eye sees the aiming point on the target, whereas in a red dot sight, the eye perceives the red dot between the target and the eye. Therefore, the eye sees clearly either the target or the red dot, but not both. In practice, the difference isn't substantial, but when using a magnifier, one may notice that in a holographic sight, the dot remains small despite looking through the magnifier, meaning the target grows but the dot does not. In a red dot sight, however, both the dot and target grow with magnification.

There is a difference, but these are generally matters of personal opinion and preference.